This is exactly why I was curious about what "rude" behavior people were talking about. What is polite/correct to one person may be considered rude to someone else.My parents' generation would/does everything for show, meaning that you tell people what you think they want to hear and then you talk smack about them behind their backs the entire time...only for you to find out later that "everybody" has been gossiping about you and has drawn stupid conclusions about you. But sure, here's a nice cheese plate & jello salad to go with your side of 'stab you in the back.' You know what's rude? Being mad/upset at someone and talking to literally EVERYONE ELSE about your issue instead of discussing it 1-on-1 directly with the person.
The people you refer to would likely go off about how "rude" a person was for asking to sit down and calmly discuss a conflict so they could find a resolution and prevent the same misunderstanding from happening in the future. How dare they be so bold in trying to have an actual conversation? Don't they know the "polite" thing to do would be to hold a grudge for years and talk about the person behind their back?

I do think there's also a cultural shift in what is considered being "respectful" to elders. I think in the past there was this mentality that young people should be silent regardless of how awful an older person is being. To people of that mindset, it doesn't matter how polite/calm/well intentioned the young person is, they are automatically dismissed as being "rude". My grandfather had a habit of belittling my mom (comparing her to her sister, constantly insulting her looks, etc) to the point of her crying. I once said, "Can you please stop being so mean? Can't you tell that you are hurting her feelings?" I was beaten and grounded for being "unbelievably rude and disrespectful" over it. If my children are ever in a similar situation where no one else was standing up for someone, I would be proud of them for speaking up. I don't see anything rude about it.